Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$6.63	13.696%	$7.538	$7.54	$7.55	$7.50
Purchase #2	$85.75	3.356%	$88.6278	$88.63	$88.65	$88.60
Purchase #3	$78.53	5.434%	$82.7973	$82.80	$82.80	$82.80
Purchase #4	$173.32	13.358%	$196.4721	$196.47	$196.45	$196.50
Purchase #5	$16.34	8.516%	$17.7315	$17.73	$17.75	$17.70
Purchase #6	$130.25	9.265%	$142.3177	$142.32	$142.30	$142.30
Purchase #7	$238.29	11.795%	$266.3963	$266.40	$266.40	$266.40
7 purchase totals =	$729.11		$801.8807	$801.89	$801.90	$801.80